Identification of quantitative trait loci (QTLs) for the characters of vascular bundles in peduncle related to indica-japonica differentiation in rice (Oryza sativa L.)

The number of vascular bundles in peduncle and the ratio of vascular bundles to primary rachis branches (V/R ratio)distinguishable between indica andjaponica, are the traits associated with the processes of differentiation between indica and japonica inrice (Oryza sativa L.). In this paper a doubled-haploid population derived from the F₁ hybrid of a cross between anindica cultivar and a japonicacultivar was used to map quantitative trait loci(QTLs) controlling numbers of vascular bundles in peduncle, primary rachis branches and the V/R ratio. For vascular bundles, three QTLs were detected and they collectively explained 58.8% of the total variation. Among them, the QTLqVB-8 with the largest effect,located on chromosome 8, individually accounted for 31.1% of the total variation. Two QTLs controlling primary rachis branches, located on chromosome 8and 10 respectively, were identified and they individually explained 10.5% and18.0% of the total variation respectively. Three QTLs for the V/R ratio, mapped on chromosome 1, 2 and 8, respectively,jointly explained 61.3% of the total variation. Of the three QTLs, the QTL qV/R-1 with the largest additive effect,explained 25.3% of the total variation,was located on chromosome 1 and found to be closely linked to the gene sh-2, a major gene underlying grain-shattering ability. In addition, four and two pairs of significant epistatic QTLs were detected for vascular bundles and the V/R ratio,respectively, but none for rachis branches. Our results suggested that the numbers of vascular bundles and primary rachis branches were independently controlled by different polygenic systems, but the two polygenic systems shared a fraction of quantitative trait loci. The present study also demonstrated that the chromosome region carrying the QTL qV/R-1 for the V/R ratio and the gene sh-2 might play an important role in the processes ofindica-japonica differentiation in rice (Oryza sativa L.). This revised version was published online in August 2006 with corrections to the Cover Date.     

Variations of the vascular bundle system in Asian rice cultivars

Summary The capacity of vascular bundle system transporting assimilates from source to sink is one of the limiting factors for rice (Oryza sativa L.) yield. Genetic variation in vascular bundle system should be investigated for improvement of transporting efficiency. A total of 531 Asian rice cultivars were studied for vascular bundles in the peduncle and its relation to spike morphology. A few difference was detected for the number of primary rachis branches of the spike among the cultivars from various countries. However, the number of vascular bundles significantly differed among the cultivars; those from Nepal, Bangladesh and India bore more vascular bundles than those from Japan. Therefore, the ratio of vascular bundles to rachis branches (V/R ratio) was nearly 1.0 in cultivars from Japan, while those from Nepal, Bangladesh and India ranged from 1.3 to 2.2. Chinese and Indonesian cultivars incuded two types of high and low V/R ratios. Cultivars with high V/R ratio showed positive reactions to the phenol solution, while those with low V/R ratio were negative reactions, suggesting that the former cultivars are of Indica type and the latter of Japonica type. It was concluded that the relationship between vascular bundles and rachis branches differentiated among the ecotypes of Asian cultivated rice.     

Genetic studies on the interspecific cytoplasm substitution lines of an Asian perennial strain of Oryza rufipogon Griff. and O. glaberrima Steud.

Summary It is shown that the restorer gene Rf _j extracted from the Japanese rice variety Akebono is effective on pollen restoration in the cytoplasm substitution line having the nucleus of Oryza glaberrima and japonica or indica cytoplasm of O. sativa, and is of the sporophytic type.The Asian perennial type of the wild rice species O. rufipogon is considered to be the progenitor of O. sativa. Two substitution lines having the cytoplasm of a perennial strain of O. rufipogon from Sri Lanka and the nucleus of O. glaberrima with or without the gene Rf _j in homozygous condition have been bred by means of successive backcrosses. These lines have now reached the BC₅ generation. Plants of the lines resemble morphologically the recurrent parent, but do not show pollen restoration, indicating that the cytoplasm of the rufipogon strain induced male sterility and that the gene Rf _j does not act as the restorer.     

Characterization of flowering time and SSR marker analysis of spring and winter type Brassica napus L. germplasm

Flowering dates and life forms of all available Brassica napus accessions conserved at the North Central Regional Plant Introduction Station (NCRPIS) were characterized, and a survey of molecular variation was conducted by using simple sequence repeats (SSR) in order to support better management of accessions with diverse life forms. To characterize flowering phenology, 598 B. napus accessions from the NCRPIS collection were planted in Iowa and Kansas field sites together with a current commercial cultivar and observed for days to flowering (first, 50% and 100% flowering) in 2003. Days from planting to 50% flowering ranged from 34 to 83 in Iowa and from 53 to 89 in Kansas. The mean accumulated growing degree days (GDD) to 50% flowering were 1,997 in Iowa, and 2,106 in Kansas. Between locations, the correlation in flowering time (r = 0.42) and the correlation in computed GDD (r = 0.40) were both significant. Differences in flowering-time rank were observed for several accessions. Accessions that failed to flower in Iowa in a single growing season comprised 28.5% of the accessions; of the flowering accessions, 100% plant flowering was not always achieved. Accessions were grouped according to flowering time. A stratified sample of 50 accessions was selected from these groups, including 10 non-flowering and 40 flowering accessions of diverse geographic origins and phenological variation. The flowering time observed in the sampled accessions when grown in the greenhouse were found to be significantly correlated to the flowering time observed in the field locations in Iowa (r = 0.79) and Kansas (r = 0.49). Thirty SSR markers, selected across 18 Brassica linkage groups from BrassicaDB, and 3 derived from Brassica expressed sequence tags (ESTs) were scored in the stratified sample. An average of three bands per SSR primer pair was observed. Associations of SSR marker fragments with the life forms were determined. Analysis of molecular variation by using cluster analysis and ordination resulted in recognizable, distinct groups of annual and biennial life-form types, which may have direct applications for planning and management of future seed regenerations. Mention of commercial brand names in this paper does not constitute an endorsement of any product by the U.S. Department of Agriculture or cooperating agencies.     

Genetics of leaf rust resistance in 13 accessions of the Watkins wheat collection

Summary The inheritance of leaf rust resistance was studied in 13 accessions of the A.E. Watkins wheat collection. Eight of the accessions (V409, V624, V628, V712, V731, V734, V745, and V855) were shown to have gene Lr33 and four of these (V409, V624, V628, and V731) also have LrW. Accessions V624 and V338 have LrB, and V377 and V488 have Lr11. V46 has an unidentified gene that gives an intermediate level of resistance. V860 has a partially dominant gene that gives a fleck reaction to avirulent isolates in the seedling stage. This gene is different from LrW and may be previously unidentified. It has been assigned the temporary gene symbol LrW2. In addition to seedling-effective genes, V46, V731, and V745 may have Lr34 and V745 may have Lr13. The adult-plant resistance in V488, V624, and V860 could not be identified. Seedling gene LrW2 and some of the adult-plant resistance should be useful sources of resistance.Contribution NO. 1576.     

Wild Oryza species as potential sources of drought-adaptive traits

Wild species of Oryza may serve as sources of superior drought tolerance alleles for cultivated rice. In a series of three screenhouse experiments, we compared traits associated with leaf water status, stomatal conductance, membrane stability, and root development in several wild Oryza accessions and O. sativa cultivars, when grown under well-watered or water-deficient conditions. One accession of O. longistaminata had greater stomatal conductance under stress and maintained leaf elongation better under stress than most other genotypes. Several upland-rice cultivars from the japonica subspecies also maintained greater conductance and leaf expansion than an indica cultivar or O. rufipogon accessions. Leaves of an accession of O. latifolia were particularly sensitive to water deficit. Oryza longistaminata and several O. rufipogon accessions had greater membrane stability, measured as electrolyte leakage from leaf disks after heat treatment, than cultivated rice. Drought treatments tended to reduce the levels of electrolyte leakage observed. Wild species had levels of osmotic adjustment under stress that were similar to O. sativa. Entries differed in the growth of roots with water deficit:O. longistaminata accessions and some japonica cultivars showed either an increase in total root mass or an increase in the proportion of root mass in deeper soil levels when water deficit was imposed, whereas indica cultivars and O. rufipogon accessions did not. Changes in root mass and distribution were correlated with values of stomatal conductance and leaf elongation; this suggests that leaf measurements made at key times in the drying cycle may reveal possible genetic differences in rooting behavior, which are otherwise difficult to measure. These studies indicate that O. longistaminata and O. rufipogon may serve as sources of novel alleles for improved leaf traits under drought stress–specifically, for maintenance of leaf elongation, stomatal conductance, and membrane stability. Alleles for improved root growth and distribution under water deficit exist in some japonica rice cultivars.     

New sources of major gene resistance in Lactuca to Bremia lactucae

Summary A total of 1789 accessions of several lettuce collections was screened to find new major gene resistance to the downy mildew fungus Bremia lactucae Regel. The accessions belonged to the species Lactuca sativa (N=1288), L. serriola (N=399), L. saligna (N=52) and L. virosa (N=50). A total of 20 races of B. lactucae were used, 14 of which were NL-races, isolated from cultivated lettuce in the Netherlands. The other six races were isolated from wild L. serriola in Czechoslovakia. The accessions were initially screened with two races: NL1 and NL3. Accessions with resistance to one or both of these races were tested with the other races. Phenotypes with new resistance were found in accessions of all four Lactuca species. Of L. sativa, four accessions were found with resistance phenotypes that could not be explained by combinations of known major genes. Many accessions of L. serriola had resistance phenotypes that indicated the presence of unknown resistance genes. All interactions between accessions of L. saligna and races of B. lactucae were incompatible in leaf disc tests, except for four accessions, which showed some sporulation with race NL6. Several accessions of L. virosa were resistant to all races used. Other accessions of L. virosa gave a race-specific interaction with B. lactucae.     

Resistance to Spodoptera litura (Fabr.) in Helianthus species and backcross derived inbred lines from crosses involving diploid species

Spodoptera litura (Fabr.), the tobacco caterpillar, is a major defoliator on sunflower in the tropics. Genetic variability for resistance to S. litura is limited in the cultivar germplasm of sunflower. In the present investigation, 43 accessions of 17 wild Helianthus species of the annual and perennial habit groups were evaluated along with cultivated sunflower under field and no-choice conditions in the laboratory for resistance to this pest. Under field conditions, H. occidentalis and H. argophyllus were found to be immune with no leaf damage and few accessions of the species belonging to section Divaricati were found to be resistant. Laboratory bioassays against neonate, two and 4-day-old larvae confirmed resistance both in terms of high larval mortality and low larval weight gain in eight species viz., H. occidentalis, H. argophyllus, H. tuberosus, H. maximiliani, H. mollis, H. simulans, H. divaricatus and H. hirsutus. Intra-accessional variability was observed and accessions of few species showed varied reaction (resistant, partially resistant to susceptible) to the target pest. Field evaluation of 224 backcross derived inbred lines from five cross combinations involving diploid species under high natural pest incidence revealed low damage in plants derived from crosses involving H. argophyllus and H. petiolaris.     

Identification and transfer of a new cytoplasmic male sterility source from Oryza perennis into indica rice (O. sativa)

Summary Most of the commercial hybrids of indica rice are based on wild abortive (WA) source of cytoplasmic-genetic male sterility (CMS). Such cytoplasmic uniformity may lead to genetic vulnerability to disease and insect pests. To overcome this problem, diversification of CMS sources is essential. Crosses of 46 accessions of O. perennis and two accessions of O. rufipogon as female parents were made with two restorers (IR54, IR64) of WA cytosterility. Sterile hybrids were backcrossed with the respective recurrent parents. Of all the backcross derivatives, one line having the cytoplasm of O. perennis Acc 104823 and the nuclear background of IR64 was found to be stable for male sterility. The newly developed CMS line has been designated as IR66707A. This line is completely sterile (0% seed set) under selfed conditions. Crosses of IR66707A with 10 restorers of WA cytoplasm showed almost complete (93–100%) pollen sterility, indicating that the male sterility source of IR66707A is different from WA sterility. Southern hybridization of IR66707A, O. perennis (cytoplasmic donor), IR66707B (maintainer) and V20A (WA cytoplasm) using mitochondrial DNA specific probes (5 endonucleases × 8 probes) showed identical banding patterns between IR66707A and O. perennis. However, in more than half of the combinations, different banding patterns were observed between IR66707A and IR66707B and between IR66707A and V20A. The results suggest that IR66707A has the same cytoplasm as the donor (O. perennis), and CMS may not be caused by any major rearrangement or modification of mtDNA. The new CMS source identified will be useful in cytoplasmic diversification in hybrid rice breeding.     

Allozyme variation and conservation genetics of common wild rice (Oryza rufipogon Griff.) in Yunnan, China

In order to reveal levels and distribution of genetic variation within Oryza rufipogon Griff. of Yunnan, China, where one of the centers of genetic diversity for Asian cultivated rice O. sativa L. is located, allozyme variation encoded by 22 loci was electrophoretically analyzed in 149 individuals of all three existing populations as well as five from other regions (Guangxi, Hainan and Jiangxi provinces) of China. As compared to the level of genetic diversity (the mean A = 1.2, P = 24.1%, Ho = 0.045 and He = 0.079) for the populations from other regions, a rather low genetic diversity (the mean A = 1.1, P = 7.6%, Ho = 0.007 and He = 0.011) was found in Yunnan, which may originate from marginal nature of these populations, recent reduction of populations and consequent drift. The result suggests that the current center of genetic diversity for O. rufipogon fail to agree with that for cultivated rice in China. The genetic differentiation for all the eight populations(F_ST = 0.254) was slightly lower than that for three populations from Yunnan (F_ST = 0.302), indicating a fairly high genetic differentiation in the region. Finally, a conservation plan for sampling/preserving fewer populations but more individuals from each population for the species was given, and an appropriate strategy for conserving the three surviving populations from Yunnan was proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cold tolerance at the early growth stage in wild and cultivated rice

The present study was conducted to understand the pattern of variation and the genetic bases for cold tolerance at the early growth stage in Asian rice. The genetic variation was investigated at the germination, plumule and seedling stages among 57 strains including cultivated rice (Oryza sativa ssp. indica and ssp. japonica) and its wild progenitor (Oryza rufipogon). The significant differentiation of cold tolerance was observed among the taxonomically divided groups. At the germination stage, both indica and japonica subspecies tended to be more tolerant than O. rufipogon, whereas at the plumule and seedling stages, ssp. japonica tended to be more tolerant than ssp. indica and O. rufipogon. Furthermore, in cold tolerance at the plumule stage, the clinal variation across the latitude of origins was observed within O. rufipogon and ssp. japonica, suggesting that the current pattern of variation seems to have been shaped by both their phylogenetic histories and on-going adaptation to the local environments. QTL analysis between O. sativa ssp. japonica (tolerant) and O. rufipogon (susceptible) revealed five putative QTLs for cold tolerance at the plumule and seedling stages but not at the germination stage. Substitution mapping was also carried out to precisely locate the two major QTLs for cold tolerance at the plumule stage, which could be used for improvement of tolerance to cold stress in ssp. indica.     

Antibiosis and antixenosis to Rhopalosiphum padi among triticale accessions

Tests for antibiosis and antixenosis resistance to Rhopalosiphum padi L., the bird cherry-oat aphid, were conducted among four wheat (Triticum aestivum L.) and eight triticale (XTriticosecale Wittmack) accessions. Tests for antibiosis included measuring R. padi-population growth over 13 days, number of days to reproduction of individual R. padi, and number of aphid progeny produced in the first 7 days of adulthood. Antixenosis was measured in no-choice nymphiposition tests and in choice tests of host selection by winged R. padi. Three of seven triticale accessions limited R. padi populations relative to control accessions. Lower R. padi-population growth on N1185 and Okto Derzhavina could be explained partially by increased developmental times. Lower R. padi-population growth on triticale accessions N1185, N1186 and Okto Derzhavina could be explained at least partially by fewer aphid progeny on these accessions. Developmental time of R. padi on N1185 and Okto Derzhavina was greater than that on Stniism 3 triticale, identified previously as resistant to R. padi. There were less R. padi progeny on N1185 than on Stniism 3, and comparable numbers of R. padi progeny among N1186, Okto Derzhavina, and Stniism 3. None of the accessions limited nymphiposition by R. padi. Choice tests revealed heterogeneity in host selection by R. padi but an overall trend that triticale accessions Okto Derzhavina, N1185, N1186 and Stniism 3 were less preferred hosts than Arapahoe wheat. Relatively strong resistance in these triticale accessions warrant consideration of their future use in breeding programs for cereal-aphid resistance.     

Identification and characterization of new sources of cytoplasmic male sterility in rice

Search for male sterility-inducing cytoplasm in wild species of the genus Oryza was attempted with a view to diversify the base of the cytoplasmic genetic male sterility system currently used in the development of commercial rice hybrids. A total of 132 interspecific crosses were made involving accessions of four wild and two cultivated species, all belonging to the A genome. Wild accessions possessing sterility-inducing cytoplasms were identified following reciprocal and sterile F₂ backcross methods. Sterile segregants were pursued through substitution backcrosses to develop cytoplasmic male-sterile (CMS) lines. CMS lines were developed with the cytoplasm of either O. rufipogon (VNI) or O. nivara (DRW 21018, DRW 21001, DRW 21039, DRW 21030 and RPW 21111). Based on shape, staining, and abortive pattern of pollen and also on type of interaction with a set of restorers and maintainers for known cytoplasmic male steriles of WA source (V 20A), the newly-developed CMS lines were grouped into four classes. Of these, RPMS 1 and RPMS 2 showed gametophytic male sterility with a restorer reaction different from WA cytoplasmic male-sterile stocks.     

Proteinase inhibitor polymorphism in the genus Vigna subgenus Ceratotropis and its biosystematic implications

The diversity of components for fourproteinase inhibitors found in species ofthe genus Vigna subgenus Ceratotropis are described. Trypsin,chymotrypsin, subtilisin and cysteineproteinase inhibitors were analyzedby isoelectric focusing followed by thegelatin replica method. Of these proteinaseinhibitors, trypsin inhibitors showedmost polymorphism both within and betweenspecies. Many trypsin inhibitor componentswere also active to chymotrypsin. Severalaccessions had very low levels or absenceof some inhibitors, such as very low levelsof trypsin inhibitor in two accessions ofthe V. tenuicaulis and absence ofchymotrypsin inhibitors in V.grandiflora and V. subramaniana.Proteinase inhibitor polymorphism broadlyagreed with the taxonomic system for thesubgenus Ceratotropis. Based oninhibitor variation species analyzed couldbe divided into three groups whichcorresponding to sections Aconitifoliae, Angulares and Ceratotropis. Some species have verylittle variation in trypsin inhibitorsdespite wide distribution, such as, V.radiata and V. reflexo-pilosa.Accessions of other species showedconsiderable intraspecific variation fortrypsin inhibitors, such as, V.grandiflora, V. aconitifolia andV. stipulacea. Proteinase inhibitorpolymorphism provides an indication of thespecies that may have contributed a genometo the tetraploid species, V. reflexo-pilosa.     

Chloride tolerance in soybean and perennial Glycine accessions

Diversity for chloride tolerance exists among accessions of perennial Glycine. Accessions whose tolerance thresholds exceed those of Glycine max cultivars may be useful germplasm resources. Soybean cultivars including ‘Jackson’ (sensitive) and ‘Lee’ (tolerant) and 12 accessions of perennial Glycine were evaluated for sodium chloride tolerance after 14 days in hydroponic culture at 0, 5, 10, and 15 g L^-1 NaCl. Sodium chloride had adverse effects on the growth of G. max cultivars and perennial Glycine accessions; however differential responses to salinity were observed among accessions. Considerably greater variation in sodium chloride tolerance existed among the perennial Glycine accessions than among the G. max cultivars. Sodium chloride tolerance thresholds ranged from 3.0 to 17.5 g L^-1 NaCl for the perennial accessions but only ranged from 5.2 to 8.0 g L^-1 for the cultivars, based on a Weibull model of leaf chlorosis. All G. max cultivars were severely injured or killed by NaCl at 10 g L^-1 and above. Five tolerant perennial Glycine accessions, G. argyrea 1626, G. clandestina 1388 and 1389, and G. microphylla 1143 and 1195, were significantly lower in leaf chlorosis score than any of the G. max cultivars at the 10 g L^-1 NaCl treatment. Two accessions, G. argyrea 1626 and G. clandestina 1389 were able to tolerate 15 g L^-1 NaCl with only moderate visual injury while all other accessions were severely injured or killed at this salt level. Variability for chloride tolerance observed among the perennial Glycine accessions has potential utility for developing enhanced salt tolerance in soybean. This revised version was published online in July 2006 with corrections to the Cover Date.     

Variation for agronomic characteristics in Crambe hispanica, a wild relative of Crambe abyssinica

Summary In order to assess the potential of Crambe hispanica, either in breeding programmes of C. abyssinica or as an oilseed crop in itself, 36 accessions of C. hispanica (29 of var. hispanica and 7 of var. glabrata) were grown in a greenhouse and evaluated for morphological characteristics, earliness, plant habit, seed characteristics and fatty acid composition. Four lines of C. abyssinica were included for reference. The 29 accessions of var. hispanica showed significant variation for all observed characteristics. Besides morphological characteristics, large variation was found for earliness, number of primary branches, seed yield, 1000 seed weight and volume, and linoleic, linolenic and erucic acid content. Morphological characteristics, earliness and plant habit did not show any high correlations with seed characteristics or fatty acid composition, except for seed hull (pericarp) mottling, which was related to a high oil and erucic acid content. The seven accessions of var. glabrata showed little variation. The large genetic variation in combination with promising figures for several characteristics, found in C. hispanica, may be useful in breeding programmes of the oilseed crop C. abyssinica, for which the available genetic variation is limited. Prospects of selection for high-erucic acid genotypes are discussed. Compared to C. abyssinica, both botanical varieties of C. hispanica are characterized by a cordate shape of the basal leaves, lack of seed retention and a lower DNA content. Plants of var. glabrata differed from var. hispanica in a sparsely hispid upper leaf surface and round stems and branches covered with a waxy layer. These clear differences and lack of success in intercrossing both varieties of C. hispanica strongly suggest that their taxonomic classification should be reconsidered.     

Molecular marker diversity and bacterial wilt resistance in wild <Emphasis Type="Italic">Solanum commersonii</Emphasis> accessions from Uruguay

Solanum commersonii is a wild tuber-bearing species native to Uruguay with high potential for use in potato breeding programs. Little is known about the genetic diversity within this wild species and the relationship with the resistance to the bacterial pathogen Ralstonia solanacearum. We studied 30 S. commersonii clonal accessions, 20 of which were collected from geographically different areas across the country, while the other ten were grown from seeds from a single plant. Resistance against R. solanacearum was tested and different levels of resistance were found, ranging from delayed wilting to asymptomatic reactions. The genetic variation and the relationships among individuals in this germplasm collection were studied by different molecular markers: Random Amplified Polymorphic DNA (RAPD), Amplified Fragment Length Polymorphism (AFLP) and Microsatellites or Simple Sequence Repeats (SSR). AFLP markers generated the largest number of total and polymorphic fragments per assay unit while SSR revealed the highest frequency of polymorphic bands (100%), followed by AFLP (96.2%) and RAPD (89.4%). In contrast, when comparing the number of different genetic profiles generated, the SSR markers exhibited the lowest discriminatory power. The clustering pattern obtained with the three marker systems showed a similar distribution of the S. commersonii germplasm revealing a high correlation between the three methods employed. All three dendrograms grouped most of the accessions into two main clusters, containing the same accessions regardless of the marker type. Bacterial wilt resistant accessions were present in both clusters. Accessions originated from different seeds of the same plant were grouped within one of the major clusters, and differed in the response to R. solanacearum revealing segregation of resistance. Furthermore, the distribution in two main clusters showed high correspondence with the geographical origin of the accessions, from the north and south of the country, and with the subspecies malmeanum and commersonii morphologically identified.     

Screening relatives of wheat for snow mold resistance and freeing tolerance

Four hundred and eighty one accessions of species and subspecies of genera Triticum and Aegilops were evaluated for resistance to speckled snow mold caused by Typhula ishikariensis and for freezing tolerance. All Triticum and seven of Aegilops species were severely affected by snow mold. Among surviving Aegilops spp., only the Ae. cylindrica accessions exhibited resistance similar to that of the most resistant winter wheat cultivar, PI 173438. After repeated screening of accessions of Ae. cylindrica, 12 accessions were identified as having resistance similar to that of PI 173438; eleven of those were considered more freezing tolerant than PI 173438, but less than wheat cv. Valjevskaya, the freezing tolerant check. Accessions of Ae. cylindrica with snow mold resistance exceeding that of PI 173438, and with freezing tolerance, are currently being screened. This revised version was published online in August 2006 with corrections to the Cover Date.     

Estimation of the outcrossing rate for annual Asian wild rice under field conditions

The Asian wild rice, Oryza rufipogon, has partial outcrossing behavior and shows high levels of genetic variation. To estimate an accurate outcrossing rate of annual form of O. rufipogon, two backcross lines (Lines R1 and R2) between Oryza sativa Nipponbare and O. rufipogon W630 were examined under field conditions. A chromosome survey confirmed that these lines had wild chromosomal segments at more than 92% of marker loci. As for the traits of glume, stamen and pistil, Line R1 showed similar floral morphology as that of O. rufipogon W630, whereas Line R2 had larger glumes. In 2005, 2006 and 2008, a total of 22 backcross plants were planted in the middle of wild rice plots. The successive progenies of each plant were examined using microsatellite markers that could clearly detect self-pollination and outcrossing. The outcrossing rates of Line R1 plants ranged from 4.04% to 25.50% with an average of 10.20%. This indicates that cross-pollination of wild rice is a chance event affected by many environmental factors. The outcrossing rates of Line R2 plants also varied, however, no significant difference was observed between the averages of Lines R1 and R2, suggesting that the glume sizes are not critical for outcrossing ability.     

Sources of resistance to diseases of sugar beet in related <Emphasis Type="Italic">Beta</Emphasis> germplasm: I. Foliar diseases

Resistance to four foliar diseases of sugar beet (Beta vulgaris ssp. vulgaris), virus yellows caused by Beet mild yellowing virus (BMYV) and Beet yellows virus (BYV), powdery mildew (Erysiphe betae) and Cercospora leaf spot (Cercospora beticola), was assessed in up to 600 accessions of closely related wild and cultivated Beta species. Most accessions were from the Section Beta, a taxon containing types most closely related to, and sexually compatible with, sugar beet and therefore most valuable for use in crop improvement. Between 1–12% of accessions were highly resistant (resistance scores of 2 on an international standardised resistance scale of 1–9) to these diseases. These levels, however, underestimate the potential number of resistant sources available from this section as some accessions with intermediate mean resistance scores contained a significant proportion of highly resistant plants within segregating populations. Variation in resistance to all diseases except BYV was observed within the Section Beta. Much higher levels of resistance were observed, and more frequently, in more distantly related sections of the genus Beta. Accessions of the Section Corollinae were highly resistant to both viruses (>62% of accessions tested), but less so to Cercospora (15%) and they were very susceptible to powdery mildew. Section Procumbentes accessions were highly resistant to BMYV and Cercospora (100%) but less so to powdery mildew (50%) and BYV (20%). However, sexual incompatibility between these sections and sugar beet make utilisation of these sources impractical using conventional breeding methods.